no BIRDS' NESTS 



several feet from the open air. The Common Wheat- 

 ear very frequently selects a crevice in a stack of peat 

 for a nesting site — a purely artificial position, and one 

 that indicates a change in selection v/ithin compara- 

 tively recent times. Another typical group of rock- 

 builders are contained in the genus Monticola. These 

 are the Rock Thrushes, birds somewhat closely allied 

 to the Chats and the Redstarts. They are dwellers 

 among the rocks, and place their nests in holes of 

 them. These nests are made on precisely the same 

 model as those of the Chats, being loosely made of 

 dry grasses, roots and moss, and lined with finer 

 fibres, hair, and feathers. A hole in a rock, or a 

 hollow beneath a boulder, or in a heap of stones, is 

 frequently chosen, whilst the materials of the nest 

 vary a good deal according to local conditions, the 

 softer linings being often omitted in districts where 

 such are difficult to obtain. Many of the closely 

 allied Redstarts {RuticiUa) make very similar provision 

 for their eggs, placing their cup-shaped nests in holes 

 and crevices of rocks, and forming them of like 

 materials. These birds occasionally find a substitute 

 for a rock in some hole in a tree — a trait common to 

 various other species normally breeding in the former 

 sites. Again, some of the Accentors {Accentor) make 

 their cup-shaped nests in holes of rocks, whilst that ex- 

 quisitely beautiful bird, the Wall Creeper (Tichodroma 

 muraria), constructs its nests in rock crevices, an open 

 structure fabricated of moss and grasses and hairs, 



